In the production of rubber compositions such as natural rubber and synthetic rubber, a highly aromatic mineral oil is used because it has high affinity for a rubber constituent, imparts extensibility and workability to rubber compositions and excels economic performance. For example, an extender oil is compounded into synthetic rubber such as SBR in its synthesis, and a process oil is compounded into a processed product of rubber such as a tire so as to improve its workability and quality of the processed product of rubber (for example, Patent Literature 1).
In Patent Literature 1, the use of petroleum process oil having the content of aromatic hydrocarbon (CA of ASTM D3238 (n-d-M analysis method)) of 20 to 35% by weight, the glass-transition temperature Tg of −55° C. to −30° C., and the kinematic viscosity at 100° C. of 20 to 50 mm2/s is proposed. When rubber obtainable by compounding this petroleum process oil into diene rubber is used for a tire, both of a fuel-efficient property and a grip property may be achieved, and heat aging resistance and heat abrasion resistance may be improved.
Furthermore, regarding asphalt pavement, in order to reclaim deteriorated and solidified asphalt when recycling asphalt scrap collected in repair of a paved road, a highly aromatic mineral oil such as a rubber compounding oil is used as a reclamation additive, and a process oil having a high aromatic content is required so as to improve a reclamation effect with small amount of addition.
Rubber compounding oils include mineral oils having various compositions, and rubber compounding oils derived from extract are known (for example, Patent Literature 2). However, since extract is generally produced by lubricant oil production equipment, there is a limit on its production volume, and as demand of rubber compounding oils is increased as recycle of asphalt pavement progresses, production by other methods has been expected.